The purpose is to present the event of the aneurysmatic disease within the polymorphism of Klippel–Trenaunay syndrome (KTS), that differs from classic forms with predominates of arteries’ lesion. Materials. The modern diagnostic of phacomatoses, including KTS, is based on physical examination. However, along with a combined lesion of skin, nervous system, internal organs, there is clinical polymorphism and delayed symptoms that hinders the verifcation of nosological entity. In the reported case the lack of objectivation of KTS’ manifestation became the cause of delayed diagnostic of aneurysmatic disease within the basic disease. Conclusion. The necessity of complex approaches in the studying of arterial hypertension and early detection of intracranial complications in patients with phacomatoses are determined by high level of intracerebral nontraumatic hemorrhage.